If you need to communicate with each other during the day, try this:

Get a phone cards from the corner store in the city you are staying.
If someone is delayed, he or she will call in to a central family voicemail box (decide this in advance). This will cost only pennies per minute.
Other family members can then retrieve the voicemail.

Otherwise, for the adult family members, I think you are worrying too much. If they want to stay out late, let them do so without worrying they are keeping you up. Let your sons keep track of their children (which presumably they do at home).

I love Post-It notes and don't go anywhere without a pad. Give them each a designated number and ask them to post a note with their number on your bedroom door each and every night when they come in. If anyone is not checked-in by Midnight, get out of your robe, pull your husband out of bed, and go searching for them with a flashlight.

Patrick's "separation strategy" makes sense, and is part of our own family separation policy.

Our basic rule is that if kids get separated from adults, they STAY RIGHT WHERE THEY ARE the instant they realize they're lost. The adult(s) willl find THEM. This prevents circling around, missing each other, and otherwise kids will often stray farther and farther from the original point.

If the kid is on public transit, they would get off at the next stop and wait there; if the adult gets on without the kid, the kid waits where they are and the adult would come back for them, the kid would NOT board the next train or bus by themselves (this has never happened and now my youngest is 16 and experienced in travelling alone).

With the ages you've told us, you're really only asking for reassurance that each son and spouse are "home," this doesn't seem controlling to me.

Simplest suggestion of all: print off this thread and send it to all your company...they will immediately "get" how much your family mean to you and will never stray out of a wish to give you no stress...

Give everyone a copy of the itinery and check that they have a watch. If all the adults carry their own tickets and those of the children they are responsible for then you will be free to enjoy your trip. If you are now a grandmother then it seems like you've earned the rest. If you worry about adults then you are setting yourself up for hardship.

I would assume that the two families won't be out very late at night- everyone will be tired. How about asking your sons to call your room when they get in?
Caution: If I were on a trip with my mother and knew that she was constantly worrying about where I was, was I ok, what time would I be back,etc... it might put a damper on things.
Your sons are old enough to be out!
A note on daytime travel: asign an adult to watch one child. Kids can get "lost" if everyone else thinks someone else is watching (did tht make any sense?) When we're on a trip with our kids my husband and I keep an eye on specific kids- we have four and need to divide them up! Do not assume thath the other spouse has a kid- talk it through again and again. Transitions are the hardest times- airport, inand out of taxis, museum entrances, etc... Just divide and conquer!
But remember to enjoy yourself too!!